I'm not sure what the best pattern for cases like this is. I don't know how good the extrapolation is, it might have quite a large error in some ranges.
I have something similar for tables of p-values without extrapolation:
- mention only in docstring about the range of extrapolation (It's just lower precision than interpolation.)
- keep warning as here
- truncate (without extrapolation some packages, and some of my functions, just return the boundary value 0.25 or 0.01, for text return it would be `'<0.01'` or `'>0.25'`)

For most use cases the exact p-value outside [0.01, 0.25] doesn't really matter and just mentioning in docstring would be enough. But I guess there would be multiple testing applications, where smaller p-values are relevant and users need to be aware that those are not very precise.